Various particulate products are manufactured by processing thermoplastic resins based on their properties. Fine resin particles are useful because they can be uniformly allocated in a product so that the product expresses a uniform property. For example, vinyl thermoplastic resins, which are generally synthesized by addition polymerization, can be obtained in the form of a dispersion by suspension polymerization or emulsion polymerization. By contrast, polyester thermoplastic resins, which are generally synthesized by condensation polymerization, cannot be obtained in the form of a dispersion by any of known polymerization procedures, and is merely obtained in the form of a block. To obtain a dispersion of polyester resins, it is necessary to take an appropriate dispersing procedure.
Japanese Patent Application Publication No. 08-176310 describes a method of producing a dispersion of a crystalline polyester resin using a phase-separation solvent. This method can merely produce a coarse particle dispersion having a dispersion diameter of several to several tens μm. Therefore, this method is not suitable for preparing a particle dispersion having a volume average particle diameter of about 1.0 μm, which can be used for toner manufacture. Generally, a dispersion of a crystalline polyester resin has strong thixotropic property. Thus, a smaller dispersion diameter makes the dispersion more viscous, which requires a longer dispersing time. Such a viscous dispersion is difficult to handle.
Japanese Patent Application Publication No. 2005-084407 describes a method of producing a resin dispersion. In this method, a crystalline polyester resin and a release agent are dissolved in an organic solvent by heating, the resulting solution is cooled so that the crystalline polyester resin and the release agent are coarsely deposited, and the coarsely deposited particles are further pulverized into small particles having a dispersion diameter of about 1 μm or less.
However, this method undesirably spends a lot of time and heat energy in the processes of heating and cooling.
Adding a release agent, such as a wax, to toner is a widely-employed technique to give releasability to the toner. Japanese Patent Application Publication No. 03-149567 describes a method of producing toner in which raw materials including a release agent and a thermoplastic resin are melt-kneaded, and the melt-kneaded raw materials are cooled and pulverized into particles. In this method, it is difficult to control particle diameter of the resulting particles. When undesired fine particles are not completely removed, basic properties of the resulting toner, such as chargeability, fixability, and heat-resistant storage stability, may be poor.
Japanese Patent Application Publication No. 09-34167 describes a method of producing toner in which raw materials including a release agent and a thermoplastic resin are kneaded, the kneaded mixture is pulverized into particles, the particles are dispersed in an aqueous medium containing hydrophilic inorganic particles, and the resulting dispersion is heated to remove the solvent and obtain toner particles. This method can control the resulting toner shape.
In this method, it is difficult to control dispersion diameter of the release agent dispersed in the thermoplastic resin. When coarse particles of the release agent are undesirably immixed in the resulting toner, basic properties of the toner, such as chargeability and fixability, may be poor.